Abstract: It is important to ensure the soft soil ground stable during the rapid filling of an embankment. The controlling indexes adopted in current embankment specifications are the displacement or its rate. The fact that ground failure repeatedly occurs implies that the controlling indexes need to be reviewed and improved. In this paper, the concept of critical state line is proposed. This critical line is obtained from the figure coordinated by the two indexes of the embankment central settlement rate and horizontal displacement rate of slope toe based on a series of field data and centrifuge model test data. The critical line separates the embankment into stability and instability regions. Hence this critical line with its mathematical expression can be taken as a critical index, which can be used to identify the stability or instability states. The three indexes, i.e. the embankment central settlement rate, slope toe horizontal displacement rate and the critical line, are combined together to form an improved stability controlling standard, which is more reasonable than the current stability controlling standard, which adopts independently the above two indexes of displacement velocities.

Key words: soft soil foundation, road embankment, monitoring, centrifuge test, control standard